Electrical devices are generally regulated or controlled by electro-mechanical means such as a potentiometer or a stepping switch. For example, the intensity of a lamp may be varied by turning a potentiometer and the speed of the motor may be varied by rotating a stepping switch. Frequently, it is desirable to physically separate the components by locating the control module, e.g., the potentiometer, the stepping switch or on/off switch at a distance from the operated device, e.g., the lamp or the motor. This may be done be extending several wires between the control module and the operated device and designing the circuitry to minimize the voltage loss along the connecting wires and to correct for this voltage loss in the regulating circuit.
Another method for separating a control module from an operated device is the use of a frequency transmitter and receiver similar to those used to automatically open and close garage doors. However, these radio control systems are costly and receivers tuned to the same frequency must be physically isolated so that a transmitted signal only controls its corresponding receiver system. In addition, there is always the risk that a receiver system can be operated by an unauthorized transmitter. Therefore, the method of merely extending wires between the control module and the operated device is frequently preferred because it is less expensive, it is less susceptible to misuse, there are no physical constraints on the proximity of one operated device to another, and it affords greater security and reliability in its use.
However, there are some applications where it may be undesirable to have electrically conducting wires. For example, such applications are frequently encountered by physicians and dentists when they are examining and treating body cavities having small work areas. An example of an attempt to solve this problem is shown in U.S. Pat. No. 3,758,951. This patent describes a dental device for illuminating an oral cavity by light transmitted on a fiber optic cable wherein the transmitted light is adjustable by a potentiometer in a control module that is located remote from the receptacle containing the light source. However, there may be some risk and attendant reluctance to use such a design if it is possible for a physician or dentist to transmit a shocking charge to themselves, or the patient in the event of a malfunction of the control module. Several ground fault detector circuits have been designed to interrupt the line voltage applied to electrical devices when a malfunction of the device creates leakage currents that could injure a patient. A casual perusal of ground fault detector circuits readily indicates that these circuits are both complex and costly. Furthermore, there is some concern if they would always operate in a timely manner to disconnect line power from a malfunctioning electrical device. In any event, these circuit devices reflect the seriousness and concern of subjecting a patient to the risk of receiving an electrical shock.
Similar prohibition against the use of a voltage carrying control module may be caused by environmental factors. For example, the potential hazard of combustible gases present in mines or explosive particles present in a laboratory or a paint spraying booth must be considered when equipment is designed and purchased for such environments. Advantages inherent in the present invention overcome the aforementioned risks and hazards and provide a control module for regulating electrical devices that can be utilized in such diverse and demanding applications with reduced risk at a reasonable cost.